linux-kernel - Re: [PATCH 0/5] Rewrite Motorola MMU page-table layout

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Date:   Fri, 31 Jan 2020 11:43:27 +0000
From:   Will Deacon <will@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Greg Ungerer <gerg@...ux-m68k.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] Rewrite Motorola MMU page-table layout

On Fri, Jan 31, 2020 at 12:31:39PM +0100, Peter Zijlstra wrote:
> On Fri, Jan 31, 2020 at 11:18:24AM +0000, Will Deacon wrote:
> > > > > +static inline pgtable_t pte_alloc_one(struct mm_struct *mm)
> > > > >  {
> > > > >  	struct page *page = alloc_pages(GFP_DMA, 0);
> > > > >  	pte_t *pte;
> 
> > Does that mean we can drop the GFP_DMA too? If so, this all ends up
> > looking very similar to the sun3 code wrt alloc/free and they could
> > probably use the same implementation (since the generic code doesn't
> > like out pgtable_t definition).
> 
> Many software TLB archs have limits on what memory the TLB miss handler
> itself can access (chicken-egg issues), it might be this is where the
> GFP_DMA comes from.

Fair enough, that sounds plausible.

> I can't quickly find this in the CFV4e docs, but I'm not really reading
> it carefully either.

I can't find any code under arch/m68k/ which suggests it, but for now
I guess we should stick with the old pgtable_t definition for sun3 with
a comment (and keep the GFP_DMA in for coldfire).

Will